This ex-vivo study investigated the effect that repeated bracket displacement has on sliding friction and the magnitude of bracket displacement, and hence tooth movement, required to release bracket/archwire binding. The design consisted of an ex-vivo laboratory study. A jig was designed that allowed repeated displacement of a bracket to occur, while the resistance to sliding (friction) was measured using an Instron universal testing machine. One type of stainless steel bracket was used in conjunction with four archwire types (0.016-inch stainless steel, 0.019 x 0.025-inch stainless steel, 0.021 x 0.025-inch stainless steel, 0.019 x 0.025-inch beta-titanium) and four magnitudes of displacement. Repeated bracket displacement has a significant effect on the sliding resistance at the bracket/archwire interface (P < 0.001). The reduction in sliding resistance noted with displacement depended on the archwire. Over the range of displacements tested, there was an 85 and 80 per cent reduction associated with 0.021 x 0.025-inch and 0.019 x 0.025-inch stainless steel, respectively. For 0.019 x 0.025-inch beta-titanium and 0.016-inch stainless steel, these reductions were 27 and 19 per cent, respectively. The importance of true friction, given the likelihood of bracket and/or archwire displacements in vivo, may be lessened.
The relatively new class of dental restoratives, termed composites, contain thermosetting resin binders and various concentrations of several different types of inert fillers. Because of the difference in types and amounts of resins and fillers present in these materials, each restorative has unique surface characteristics. In addition, the various resin types and filler loading volumes cause differences in polymerization shrinkage and adaptation to the margins of cavity preparations. A combination of radioisotope leakage studies and scanning electron microscopy studies was used to investigate the surfaces and adaptation of four of these composite materials in comparison to an amalgam, silicate, and unfilled poly ( methyl methacrylate).
Four aromatic, thermosetting, composite dental restorative materials were evaluated for their mechanical and physical properties. The properties of two materials approached those of dentin and dental amalgams. One of the materials tested appeared to have the necessary requirements for use as both an anterior and posterior restorative material.
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